The present invention relates to cranes that use one or more load hoist lines to lift loads. In cranes of this type, each load hoist line is wrapped, or reeved, around a separate load hoist line drum. The drum is rotated to either pay out or retrieve the load hoist line drum. A drum drive assembly is used to rotate the drum during normal crane lifting operations.
Under certain circumstances, it is desirable to disconnect the drum from the drum drive motor so that it may rotate freely. For example, when a crane is used to repeatedly hoist objects a long vertical distance, it may be faster and/or more economical to allow the influence of gravity acting upon the hook block to pull the load hoist line off of the load hoist line drum between lifts. Once the hook block has been lowered back to the ground, the load hoist line drum is reconnected to the drum drive motor so that the load hoist line can be used to hoist the next object.
One of the purposes of the present invention is to provide a drum drive assembly which will permit the quick, easy, and safe disconnection of the load hoist line drum from the drum drive motor.